The two-particle twist-3 distribution amplitudes of
pseudoscalar meson have the expansion in the terms
of the Gegenbauer polynomials
[1]}, [2]},
\({\phi }_{P}^{p}(x)&=& 1+\Big (30{\eta }_{3}-\frac{5}{2}{\rho }_{P}^{2}\Big )C_{2}^{1/2}({\xi })-\Big (3{\eta }_{3}{\omega }_{3}+\frac{27}{20}{\rho }_{P}^{2}+ \frac{81}{10}{\rho }_{P}^{2}a_{2}\Big )C_{4}^{1/2}({\xi }), \\{\phi }_{P}^{t}(x)&=&C_{1}^{1/2}(-{\xi })+6\Big (5{\eta }_{3}-\frac{1}{2}{\eta }_{3}{\omega }_{3}-\frac{7}{20}{\rho }_{P}^{2}-\frac{3}{5}{\rho }_{P}^{2}a_{2}\Big )C_{3}^{1/2}(-{\xi }).\) 
